A chemical amplification resist composition is a pattern forming material for forming a pattern on a substrate by producing an acid in the exposed area upon irradiation with radiation such as far ultraviolet light and through a reaction using the acid as a catalyst, changing the developer solubility of the area irradiated with an actinic ray and that of the non-irradiated area.
In the case of using a KrF excimer laser as the exposure light source, a resin having small absorption in the wavelength region of 248 nm and having a basic framework of poly(hydroxystyrene) is predominantly used as the main component, and this is an excellent system capable of forming a good pattern with high sensitivity and high resolution, compared with the conventional naphthoquinone diazide/novolak resin system.
On the other hand, in the case where a light source of emitting light at a shorter wavelength, for example, an ArF excimer laser (193 nm), is used as the exposure light source, a satisfactory pattern cannot be formed even by the above-described chemical amplification system, because the compound having an aromatic group substantially has large absorption in the region of 193 nm.
In order to solve this problem, a resist composition for ArF excimer laser, containing a resin having an alicyclic hydrocarbon structure, has been developed.
As a photoacid generator that is a major constituent component of the chemical amplification resist composition, a triphenylsulfonium salt is generally known.
Furthermore, in the case of using a light source of electron beam, X-ray, EUV or the like, the exposure is performed under vacuum and therefore, an outgassing problem that a low-boiling-point compound such as solvent or a resist material decomposed by high energy volatizes and contaminates the exposure apparatus, becomes serious. Various studies for reducing outgassing are recently proceeding, and improvements have been also proposed on the photoacid generator. In addition, it is demanded to develop a photosensitive composition enhanced in the sensitivity, resolution, pattern profile, roughness performance and the like by not only reducing outgassing but also improving the photoacid generator.
For example, from the standpoint of enhancing the sensitivity, dissolution contrast, exposure latitude, roughness performance and the like, Patent Document 1 describes a photoacid generator capable of being decomposed by an acid, but more improvements are demanded in terms of dissolution contrast, developability and the like.
Among others, as the pattern dimension is smaller, the roughness property and resolution become more important. In this connection, lithography with an X-ray, an electron beam or EUV aims at forming a fine pattern of several tens of nm and therefore, the composition is required to be excellent particularly in the resolution and roughness performance.
For example, in Patent Document 2, from the standpoint of, despite low sensitivity, enhancing the resolution, roughness performance, exposure latitude and the like, a sulfonium salt having a specific betaine structure is disclosed as a photoacid generator.
However, there is a problem in the sensitivity and accordingly, in the aging stability of sensitivity.
With respect to sensitivity, an elevation of the sensitivity is a very important issue for shortening the wafer processing time, but when higher sensitivity is pursued, the pattern profile or resolution indicated by a limiting resolution line width is deteriorated, and it is strongly desired to develop a resist composition satisfying all of these properties at the same time.
High sensitivity is in a trade-off relationship with high resolution and good pattern profile, and an important issue is how to satisfy these properties at the same time. This issue needs to be solved.